Role of X chromosomal song genes in the evolution of species-specific courtship songs in Drosophila virilis group species

In the Drosophila virilis group the males of the virilis phylad species produce courtship song consisting of pulse trains with no pauses between successive sound pulses, whereas the males of the montana phylad species produce songs with clear pauses between the sound pulses. We obtained song data for F1 hybrids between D. virilis (representing the virilis phylad) or D. flavomontana (representing the montana phylad) females and the males of several species of the D. virilis group to study the interaction of X chromosomal and autosomal song genes affecting species differences in song. In crosses with D. virilis females, X chromosomal (or maternal) factors masked variation in pulse length despite variation in heterospecific autosomal song genes. To the contrary, in crosses with D. flavomontana females, X chromosomal genes largely determined the pause length and interacted with autosomal genes to determine the pulse length. In the montana phylad species, pulse length showed dominance toward shorter pulses and pause length toward longer pauses. The first-mentioned trait also indicated the epistatic effects of X chromosomal and autosomal components.